The invention relates to an improvement in devices for controlling a mechanism which produces an output level related to an input level. The devices to which the present invention relates have mechanical means for comparing the output level with the input level to produce a control level or signal. The control level is delivered by suitable transmitting means to the mechanism which produces the output level.
In particular, so-called stepping devices are known, in which the input and output levels are varied in small increments. A very high degree of precision is required in such devices.
An important advance was made in the prior art in replacing the mechanical feedback of the movements of an output member to a comparator by feedback of an electrical signal. However, there are reasons for preferring to use a mechanical feedback.
It has now been found that it is possible to obtain the same precision with mechanical feedbacks as with the electrical feedback, provided that a gear transmission is used which allows a coefficient of reduction of the movement to be achieved which is as high on the input side as on the feedback side, and which allows the taking up of play by action on bevel movement-transmission gears and on reduction gears.
If these conditions are fulfilled it is possible to use hydraulic motors for the output movement which allow rotational speeds greater than those available up to the present time to be obtained.